Liming Agents: What's the deal with all these products?

March 13, 2014 5 Comments

I get asked questions about liming agents all the time and was excited to find this old quote from ClackamasCoots dug up by TreeDog on  

Here is the full Quote with a few updates by me. 

"I just got back from a ride in the country to clear my head and I was thinking about the best way to help you with the calcium deal.

Here is a rundown on liming agents in general and what they contain.

1. Limestone - calcium carbonate 

2. Dolomite Lime - Dolomitic lime is a rock. It can be quite pretty. It is calcium magnesium carbonate, CaMg(CO3)2. It has about 50% calcium carbonate and 40% magnesium carbonate, giving approximately 22% calcium and at least 11% magnesium.

3. Gypsum - elemental calcium (Ca) and sulphur in a the form of S04 meaning that it is elemental sulphur with 4 oxygen molecules attached which is important in the CeC paradigm. (Although Gypsum really isn't a liming agent.)

4. Oyster Shell Powder - calcium carbonate (CaCo3) - This product is not what it would appear from the name, i.e. it's not a product made from crushed oyster shells but rather it's a particular oyster shell mined from the San Francisco Bay from ancient sea deposits made up of very tiny and fragile oyster shells.

5. Crushed Oyster Shells - calcium carbonate (CaCo3) and this product is made from crushed oyster shells.

As you can see, all of these liming agents either contain elemental calcium or calcium carbonate and it's the carbonate which is used to correct acid conditions in a soil.

The reason that I do not recommend using dolomite lime is that it contains 2:1 calcium to magnesium. Where as our soil's are better with closer to 5:1 - 10:1 That isn't to say the magnesium isn't important - quite the opposite it's extremely important but magnesium has absolutely nothing to do as far as a liming agent.

Excessive magnesium will cause soils to bind up making it difficult for the plant's root hairs to move through the soil to exchange their hydrogen cation (+) for minerals, macro and micro nutrients.

In plant or algea based soil amendments like alfalfa meal and kelp meal, a review of the levels of calcium vs. magnesium show that it's 4 and 5x - quite the opposite of dolomite lime.

Calcium carbonate is water soluble while magnesium is not. You can use this to your advantage by using limestone in water as part of your irrigation program. I'd recommend about 1 tablespoon per 1 gallon of water. Stir, shake, stir, shake - then apply. This will provide your plants with the amount of calcium necessary to maintain health and growth vigor.

Crushed oyster shells is also pure calcium carbonate. It can be dissolved in water but that can take several days/few weeks. This is the product that chicken growers feed to their hens both for the calcium content (to insure strong egg shells) but also for grit used the hen's gizzard to digest grains.

Oyster shell powder is pure calcium carbonate and is instantly dissolved in water.

You can use apple cider vinegar and soak the crushed oyster shells to extract the calcium carbonate. By volume you would want to mix 1x crushed oyster shells (or egg shells) with 3x apple cider vinegar and let it brew for 2 - 3 weeks. The vinegar will extract the calcium from the eggs shells in a concentrated form. Mix 1/4 cup of the vinegar with 1 gallon of water and apply to your soil.

And if you take egg shells and put them into a large pan with your Weber BBQ fired up and heat them until they turn every shade of dark brown to black and then take them and crush them and do the same deal with the crushed oyster shells, you'll end up with calcium phosphate. Apply at the same rate noted above for the crushed oyster shells. You can also process the crushed oyster shell the same way - heating until charred and then distilling the calcium out with apple cider vinegar.

While it's true that the good ol' N-P-K deal dominates the cannabis growing meme, in the world of soil science the basic study is often about the building-block cations: Calcium (Ca+2), Magnesium (Mg+2), Potassium (K+1) and Sodium (Na+1) and the acidic cations, Hydrogen (H+1) and Aluminum (Al+3)


LD " 

I like this quote because it's simple and straight forward. If anyone wants more info, this brief blog will give them the info to start doing more research on their own. 

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Thanks for reading,

Jeremy Silva

5 Responses


February 17, 2017

Hey there!
So my last soil recipe I used about 1 cup per cubic foot of Dolomite Lime for my liming agent.. my current soil (still being tweaked) is using 2 (maybe more) cups per cubic foot of the BAS Mineral Mix which consists of 2 parts Basalt, 1 part Gypsum and 1 part Oyster Shell Flour.

My question is, will this effectively replace my “typical” Dolomite Lime?

Should I use at 2 cups/cf or up to 4 cups? I am leaning toward going no-til, so this may affect things. Right now, as it stand, my current mix I have planned is as follows (based heavily on the No-Til recipe found on the GrassCity forums):

Base Soil:
-1 part Compost+EWC (25% EWC:75% Compost)
-1 Part Sphagnum Peat Moss
-1 Part Perlite (A little more than 1/3, though… maybe 40% or so at least… probably moving to lava rock or pumice, though, if I’m doing no-til)

2 (perhaps 2-4?) cups of this Mineral Mix (per cubic foot):
-2 Parts Basalt
-1 Part Gypsum
-1 Part Oyster Shell Flour

3 cups total of amendment mix (per cubic foot):
-2 parts Kelp Meal (maybe just 1 cup?)
-1 part Alfalfa Meal (possibly not needed? It’s not listed in the no-til recipe)
-1 part Crustacean Meal
-1 part Neem Meal
(The no-til calls for 1 cup each of kelp, crustacean meal and neem per cubic foot.. maybe I’ll stick to that.. still researching)

-1 cup Malted Barley Powder (per cf… in addition to the 3 cups of amendments)

so my main questions are:

1) Should this Mineral Mix be sufficient in replacing Dolomite Lime?

2) If so: What amounts should I use this Mineral Mix? I’m leaning towards a little more than 2 cups per cf, not sure if I should go as high as 4 cups as suggested?

3) Any thoughts or suggestions on my planned organic soil mix in general?

I’m moving on to No-Til from my current non-no-till soil (which is doing GREAT but still mediocre and I want to get away from Azomite), I’m wondering if I should replace the Perlite with Lava Rock or something… I’m still tweaking it but want to get this perfect.

I’ve recently decided to go full no-til (in 10 gallon smart pots… as big as I can go with those unfortunately), so I think the biggest flaw is the Perlite as I believe it can become compact over time. Pumice or Lava Rock will most likely replace this. I think I’d like to steer away from Rice Hulls as they break down as well, or so I read. Anyway, as you can see I still am researching and planning, looking for any suggestions from people with a lot of experience in this area.

Thanks!! Great post.


September 13, 2016

Do egg shells need to be extracted for their calcium carbonate or can they just replace oyster shell in a soil mix?


August 09, 2016

Hi, what so you Think of calcified Sea weed or Maerl as ph up?

Green King Organics
Green King Organics

October 27, 2015

How long does liquid calcium extracted from oysters using apple cider vinegar last? It smells a little like sulfur after a couple of months. Still good?

Jason D
Jason D

March 15, 2015

I use crushed oyster shells not the powder but the roughly crushed ones. I use this from day one in my dirt, a old dude told me about it and it worked for him very well. In Lake county we have super weather and great sun, and my garden compared to my buddies was apples and orange vodka martini’s. I also use a bit of blood meal and bat guano(I have a bat house for like 300 bat colony from my friend Mr. Hathaway in Nice he makes them, if you see the Got Bat’s sign in Nice you are there) The guano from my bats and the oyster shells calcium make a great happy plant with superfood soil. I love the old ways of mixing your dirt, using amendments for your soil not powder and potions. Happy days and a sticky ,sweet haze.

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